Heat stabilization of polyesters

ABSTRACT

IT HAS BEEN DISCOVERED THAT POLYESTERS CAN BE STABILIZED AGAINST THE SPONTANEOUS DEGRADATION WHICH THE POLYESTERS ORDINARILY UNDERGO WHEN THEY ARE HEATED TO TEMPERATURES SUBSTANTIALLY ABOVE THEIR MELTING POINTS FOR A PERIOD OF TIME BY THE INCORPORATION THEREINTO OF A SMALL AMOUNT OF ONE OR MORE 2(5H) FURANONES WHICH ARE CMPATIBLE WITH THE POLYESTER, ARE UTRAVIOLET ABSORBING, AND WHICH ARE. THEMSELVES STABLE AT SAID TEMPERATURE.

EX TRUS/O/V RATE (G/M) Feb. 22, 1972 K. T. BARKEY ETAL 3,644,573

HEAT STABILIZATION OF POLYESTERS Filed July 2, 1969 BREAKDOWN 0F VISCOSITY l l l l -$E60N05 AT 278C KENNETH T BAR/(EV C SHELBURN HUNTER ATTORNEYS I United States Patent US. Cl. 260-860 7 Claims ABSTRACT OF THE DISCLOSURE It has been discovered that polyesters can be stabilized against the spontaneous degradation which the polyesters ordinarily undergo when they are heated to temperatures substantially above their melting points for a period of time by the incorporation thereinto of a small amount of one or more 2(5H) furanones which are compatible with the polyester, are ultraviolet absorbing, and which are, themselves, stable at said temperature.

This invention relates to new and improved polyester compositions having the valuable property of being stabilized against spontaneous thermal degradation under or-' dinary polyester melt processing conditions.

It is well known that linear polyesters such as poly- (ethylene terephthalate) thermally degrade spontaneously when such materials are heated for any extended period of time at temperatures substantially above their melting points. Such spontaneous degradation reveals itself in the manner in which it aifects some of the important physical and chemical properties of the polyester material. For example, exposure of the polyester to temperatures at which it would ordinarily be extruded and/or molded or cast into some useful form (such as about 275 C. for poly(ethylene terephthalate)) for only a few minutes results in (a) the intrinsic viscosity of polyester dropping fairly sharply, (b) more unwanted carboxylic acid and aldehydic ends appearing in the polymer and (c) an undesirable brownish discoloration developing fairly rapidly in the molten material. All of these evidences of degradation are almost invariably undesirable. In fact, for some intended end uses of polyesters, the amount of loss of viscosity (and the concurrent loss of other related physical properties) that occurs over a period of time of as little as 20 minutes sometimes makes it necessary to discard the thermally degraded material. Such prolonged exposure to high temperatures can occur, for example, when an extruding machine is temporarily stopped for any of a number of possible reasons, and the machine must be maintained in the ready condition for subsequent continuation of the extrusion process.

Many attempts have been made heretofore to stabilize linear polyester material against high temperature thermal degradation. However, effective stabilizers that function under such high temperature conditions are extremely difiicult to discover. Materials that are effective stabilizers to prevent the thermal degradation of other polymeric materials such as polyethylene or polyvinyl halides are either not compatible with the polyester materials or simply do not function in the required manner at the relatively higher temperatures in which the present problem exists (since the mechanism of thermal degradation difi'ers between most polymer types). Also, many materials that are compatible with, and can be dissolved into, the linear polyester materials have either no efiect on the spontaneous thermal degradation of the polyester or have even an undesirable accelerating effect on the degradation.

It has now been discovered that the undesired spontaneous high temperature thermal degradation of linear polyesters (having repeating residue units of at least one 'ice glycol and at least one dicarboxylic acid) can be prevented by the incorporation into the polyester material of a small, but effective, stabilizing amount of one or more 2(5H) furanone materials (a) which are compatible with the polyester being stabilized, (b) which are stable themselves at temperatures of at least about 275 C., and (c) which have the structure 7 /0 0:0 \C=DWQ, A-(|3=O-B wherein A is --CN,

R being an amino, substituted amino, alkoxy, aralkoxy, alkyl, aryl, or heterocyclic substituent; B is an alkyl, aryl, aralkyl, alkaryl or H substituent; D is a methylidene radical (=CH), a polymethine chain of 2-5 carbon atoms, a p-phenylene methylidene radical, a nitrogen atom (=N), a hydrazinylidene radical, an alkylidene radical or an aralkylidene radical; W is either a carbon-carbon single bond or a methylene radical; and Q is an alkyl, aryl, substituted aryl, a heterocyclic ring or a heterocyclidene radical.

The compatibility and the stability of these 2(5H) furanones can readily be determined by melting them, for example, at a level of about 1000 ppm. together with poly(ethylene terephthalate), and holding the resulting molten mixture at a temperature of about 280 C. for 30 minutes. If the resulting mixture remains uniform in clarity, and does not develop a high degree of brownish or dark yellow color in this period of time, the furanone is both compatible and stable, in accordance with the aforementioned limitations regarding those 2(5H) furanones that can be used successfully in the practice of this invention.

The linear polyester materials (in which the problem solved by the present invention exists and to which the present invention relates) are linear polyesters of at least one glycol having 2 to 10 carbon atoms and at least one dibasic acid comprising at least 50 mole percent of an acid having two carboxyl radicals attached to a carbocyclic nucleus having from 4 to 6 carbon atoms per ring, said ester having a number average molecular weight of 10,000 to about 100,000, an inherent viscosity in a mixture of 60% phenol and 40% chlorobenzene of at least 0.3 and melting at from about C. to about 350 C.

Of the 2(5H) furanones that are useful in the present invention, several are particularly preferred. These are:

(a) 3-cyano-5-orthonitrobenzylidene-4-phenyl-2(5H) furanone (b) 5-benzylidene-4-methyl-3-p-nitrophenyl-2(5H) furanone (c) S-benzylidene-3-carbamoyl-4-phenyl-2(5H)furanone (d) 3-cyano-4-phenyl-4,5-pyridylrnethylidene-2(5H) furanone (e) 3-carbamoyl-5(Z-methylbenzylidene)-4-phenyl- 2(5H)furanone (f) S-benzylidene-S-N- ethoxycarboxy) carbamoyl-4- phenyl-2(5H)furanone (g) S-benzylidene-3-phenyl-ureido-4-phenyl-2(5H) furanone (h) S-benzylidene-3-cyano-4-phenyl-2(5H)furanone (i) 3-cyano-5-dimethylamino-methylidene-4-phenyl- 2(5H)furanone Of these, compounds g, h, i, b and d are still further preferred. A more detailed description of the 2(5H) furanone materials, including methods for their manufacture, can be found in US. patent application Ser. No. 555,240, filed June 6, 1966 and. now U.S. Pat. No. 3,507,648 issued Apr. 21, 1970. Still further preferred for use in the practice of this invention are those 2(5H) furanones which are essentially colorless; that is, which impart very little, if any, color to the polyester material when the furanone is present at the 1000 ppm. level. In this regard, particularly preferred polyester compositions contain (1) poly(ethylene terephthalate), poly(1,4-cyclohexylenedimethylene terephthalate), poly(ethylene isophthalate), poly(ethylene naphthalenedicarboxylate) or a mixture of at least two of these, as the polyester component and (2) an effective stabilizing amount of one of (or a mixture of) the compatible, stable 2(5H) furanones described above, which compositions absorb ultraviolet light in the region of 380 mm. and which compositions yield solution color values of at most about 12, when measured in the following manner:

A %by weight solution of the composition (in 60:40 phenolzchlorobenzene) is measured for percent transmission at 400 and 550 nanometer with a conventional spectrophotometer, with the solvent serving as a blank. Color value is calculated as follows:

Color value: 100 V2 (T -l- 550) In the practice of the present invention, it has been found that only a very small amount of the 2(5H) furanone material(s) of this invention need be present in the molten polyester in order for at least a small amount of benefit to be obtained. However, generally for most uses a relatively high degree of thermal stabilization of the polyester is desired. Therefore, generally at least about 50 parts per million (based on the amount of polyester present) of the valuable 2(5H) furanone material should be present in the resulting stabilized composition. While there is apparently no critical upper limit with regard to the amount of furanone that can be used to effectively stabilize the polyester compositions of this invention, generally, because of cost considerations and because sometimes the color contributed by certain of the furanones to the resulting composition is not desired, at most about 5,000 parts per million of the furanone material should be used. For optimum results, it is preferred that the total amount of furanone materials present in the polyester compositions of the present invention be within the range of from about 100 to about 2,000 parts per million.

Apparently the particular manner whereby the furanone material is incorporated into the polyester material is also not critical. The furanone can, for example, be simply physically mixed with powdered or pelletized or flaked polyester prior to the time the materials are melted together in the extruder. If desired, an intimate blend of the polyester and furanone can be prepared prior to the extrusion step by either melting the components together in a separate step or even by dissolving them together in a common solvent system and subsequently removing the solvent. In any event, apparently all that is needed to 4 effectively stabilize the polyesters with one or more of the 2(5H) furanones is to uniformly disperse (or,dissolve) the furanones material through the polyester.

Referring now to the drawing, which is illustrative of the data appearing in table one, below, in graphic form; line 1 illustrates the degradation in viscosity of poly(ethylene terephthalate) containing only conventional catalysts and stabilizers (to prevent oxidative degradation). Line 2, which has a slope that is almost flat, as compared with the slope of line 1, is illustrative of the high degree of high temperature thermal stabilization that can be accomplished by practicing the present invention. Line 3 illustrates the increase in the rate of thermal degradation that results when certain types of non-furanone chemical additives are present in the heated polyester. It should be noted that since the ordinate in the drawing represents an increase in the total amount of extruded polyester material in a given length of time, and since increasing rates result from decreasing viscosities, the steeper the slope of the curves illustrated in this figure, the poorer is the high temperature thermal stability of the composition being tested. Thus, the use of an ideal stabilizer would be expected to result in a fiat line. From the drawing and from Table 1 below it can be seen that the use of the stabilizers of this invention can very closely approximate such an ideal stabilizer.

EXAMPLES In order to evaluate high temperature thermal stabilization of polyesters, poly(ethylene terephthalate) was chosen as a typical example of such linear polyester materials. Except for the particular melting point and the actual temperature region in which spontaneous thermal degradation of the polyester takes place at an accelerated rate, other polyester materials falling within the generic description set out above are expected to yield data comparable to that which results from tests performed on pol'y(ethylene terephthalate). The intrinsic viscosity (tested in a :40 blend of phenol and chlorobenzene of the poly(ethylene terephthalate)) used in this is test initially 0.62. In the following examples all parts set out are by weight unless otherwise specified.

Ten thousand parts of powdered poly(ethylene terephthalate) are blended in a conventional stainless steel blender with ten parts of the illustrative 2(5H) furanone material (in powdered form) for 2 minutes. The resulting blend is then dried under a high vacuum (500 microns pressure) at 215 C. for a half hour. After releasing the vacuum with nitrogen and while carefully maintaining the resulting mixture under a blanket of nitrogen, the resulting mixture is transferred to a conventional melt rheometer and heated to 278 C. under a pressure of 400 lbs. Samples are periodically collected from the rheometer via a closely timed extrusion and subsequently weighed in order to obtain the data appearing in Table 1 below. The particular furanone materials tested are assigned example designations A through fD, while the control polyester material (containing no test additives) is'assigned designation E and several other somewhat chemically similar (to the furanone configuration) materials have been designated F through H in this table.

TABLE 1.-EXTRUSION DATA FCAI EI PZQJSETHYLENE TEREPHTHALATE) Time Grams] Time Grams] Time Grams Example No. (seconds) minute (seconds) minute (seconds) minute phenyl-2(5H)furanone;

phenyl-2(5H)turanone; G=3-p-nitr0anilino-l-p-nitrophenyl aminoisoindolenine; H'=-i-pbr0mophenyl-3-cyan0-2(5H)iuranone.

2 Line 3 in the drawing.

The procedure described above has made it possible to illustrate still another advantage of the compositions of the present invention. That is that the 2(5H) furanone materials will not sublime from the molten compositions. Sublimation out of the molten system of various additives has been a problem in the past, particularly for materials that might conceivably perform as the desired high temperature stabilizers. Still another advantage of the present compositions is that the compositions of this invention can prevent ultraviolet light from passing through the compositions even though the compositions might otherwise appear to be completely transparent. This latter particular aspect of the compositions of this invention can be utilized in the manufacture of valuable radiographic film units such as those described in detail in copending US. patent application Ser. No. 868,222, entitled Radiographic Elements and Products, filed Oct. 21, 1969'.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A heat-stabilized polyester composition suitable for use as a photographic film or a foil, said composition comprising a linear polyester of repeating glycol and dicarboxylic acid units having a molecular weight of at least about 10,000 and a heat stabilizing amount of a compatible, high temperature resistant, UV absorbing 2(5H) furanone having the formula:

c A( J=d-B wherein A is CN,

o JLR R being an amino, alkoxy, aralkoxy, alkyl, aryl, or pyridyl group substituent; B is an alkyl, aryl, aralkyl, alkaryl or H substituent; D is a methylidene radical (=CH-), a polymethine chain of 2-5 carbon atoms, a p-phenylene methylidene radical, a nitrogen atom (=N-), an alkylidene radical having two or more carbon atoms or an aralkylidene radical; W is either a carbon-carbon single bond or a methylene radical; and Q is an alkyl, aryl, nitro or alkyl substituted aryl or a pyridyl group.

2. A heat-stabilized composition as in claim 1, wherein said polyester is selected from the group consisting of poly(ethylene terephthalate), poly(1,4-cyclohexylenedimethylene terephthalate), poly(ethylene isophthalate), poly(ethylene naphthalenedicarboxylate) and mixtures thereof.

3. A heat-stabilized polyester composition as in claim 1 wherein said amount of said furanone is from about 50 to about 5000 parts per million, based on the Weight of said polyester in said composition.

4. A heat-stabilized polyester composition as in claim 3, wherein said 2(5H) furanone is selected from the group consisting of (a) 3-cyano orthonitrobenzylidene 4 phenyl 2- (5H)furanone;

(b) 5 benzylidene 4 methyl-3-p-nitrophenyl-2(5H) furanone;

6 (c) S-benzylidene 3 carbamoyl-4-phenyl-2(5H)furanone; (d) 3-cyano 4 phenyl 5 (4 pyridylmethylidene)-2- (5H) furanone;

(e) 3-carbamoyl-5 (2 methylbenzylidene) 4 phenyl- 2(5H)furanone;

(f) 5 benzylidene 3 N(ethoxycarbonyl)carbamoyl- (g) S-benzylidene 3 phenyl ureido-4-phenyl-2(5H) furanone;

(h) 5-benzylidene-3-cyano-4-phenyl-2(5H)furanone;

(i) 3-cyano 5 dirnethylamino-methylidene-4-phenyl- -2(5H)furnanone.

5. A film element comprising poly(ethylene terephthalate) and from about 50 to about 5000 parts per million, based on the weight of said poly(ethylene terephthalate), of a 2(5H)furanone having the structure:

R being an amino, alkoxy, aralkoxy, alkyl, aryl, or pyridyl group substituent; B is an alkyl, aryl, aralkyl, alkaryl or H substituent; D is a methylidene radical (=CH-), a polymethine chain of 2-5 carbon atoms, a p-phenylene methylidene radical, a nitrogen atom (=N-), an alky1i dene radical having two or more carbon atoms or an aralkylidene radical; W is either a carbon-carbon single bond or a methylene radical; and Q is an alkyl, aryl, nitro or alkyl substituted aryl or a pyridyl group.

6. Poly(ethylene terephthalate) film having, dissolved therein, from about to about 2000 parts per million of a 2(5H)furanone selected from the group consisting of 5-benzylidene-4methyl-3-p-nitrophenyl-2(5H)furanone;

S-benzylidene-3-carbamyl-4-phenyl-2(SI-Dfuranone;

S-benzylidene-cyano-4-phenyl-2(5H)furanone;

5 benzylidene 3 N(ethoxycarbonyl) carbamoyl 4- phenyl-2(5H) furanone; and 5-benzylidene-3-phenyl-ureido 4 phenyl 2(5H)furanone; said poly(ethylene terephthalate) having an intrinsic viscosity of from about 0.3 to about 2.

7. A heat-stabilized polyester composition as in claim 1, wherein said composition is in the form of fibers.

References Cited UNITED STATES PATENTS 3,323,930 6/ 1967 Newland et al. 106176 3,468,912 9/1969 Ford, Jr. et al. 260-3435 3,507,648 4/1970 Ford, Jr. et a1 961.6

HOSEA E. TAYLOR, Primary Examiner R. A. WHITE, Assistant Examiner U.S. Cl. X.R. 260--45.8 A, 45.8 N i mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 644,573 Dated ruary 22, 1972 Kenneth T. Barkey, C. Shelburn Hunter, Walter L. Predmore, Jr

Inventor(s It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 15, delete -CN,".

Column 5, line 37, delete "-CN,".

Column 6, line 26, delete -CN,"; line 46, delete "carbamyl" and insert --carbamoyl--.

Signed and sealed this 20th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

